Differential signaling has been in existence for many years. For example, teletypes were some of the first equipment to use differential signaling to communicate. One common technique of differential signaling utilizes a current loop to send and receive information between a receiver and transmitter.
According to this differential signaling technique, current is sent in one direction around the loop, or the other direction around the loop, to represent information. A pulse of current in the loop in one direction may correspond to a logic value of “1”, while a pulse in the opposite direction may correspond to a logic value of “0.”
Current loops have several advantages over other signaling techniques. For example, data sent utilizing a current loop can travel further than data sent through a common RS-232 interface. Current loop differential signaling techniques also provide protection against electrical interference. Additionally, current loop differential signaling techniques can reliably make connections when other communication techniques cannot.
One type of a current loop differential signaling technique is Low Voltage Differential Signaling (LVDS). LVDS is a differential signaling technique commonly used in data transmission systems. LVDS uses relatively low supply voltages; VDD is generally in the range of 2.5 volts and VSS is generally zero. The valid common-mode range for a LVDS receiver is generally between VSS+50 mV and VDD−50 mV. A low voltage differential signal produced by a line driver typically has peak-to-peak amplitudes in the range from 250 mV to 450 mV. The low voltage swing minimizes power dissipation, while maintaining high transmission speeds. Typical transmission speeds are over 100 Mbps (Mega-bits per second).